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In the debate of LlamaIndex vs LangChain, developers can align their needs with the capabilities of both tools, resulting in an efficient application.

LLMs have become indispensable in various industries for tasks such as generating human-like text, translating languages, and providing answers to questions. At times, the LLM responses amaze you, as they are more prompt and accurate than humans. This demonstrates their significant impact on the technology landscape today.

As we delve into the arena of artificial intelligence, two tools emerge as pivotal enablers: LLamaIndex and LangChain. LLamaIndex offers a distinctive approach, focusing on data indexing and enhancing the performance of LLMs, while LangChain provides a more general-purpose framework, flexible enough to pave the way for a broad spectrum of LLM-powered applications.


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Although both LlamaIndex and LangChain are capable of developing comprehensive generative AI applications, each focuses on different aspects of the application development process.


Llamaindex vs langchain
Source:  Superwise.AI


The above figure illustrates how LlamaIndex is more concerned with the initial stages of data handling—like loading, ingesting, and indexing to form a base of knowledge. In contrast, LangChain focuses on the latter stages, particularly on facilitating interactions between the AI (large language models, or LLMs) and users through multi-agent systems.

Essentially, the combination of LlamaIndex’s data management capabilities with LangChain’s user interaction enhancement can lead to more powerful and efficient generative AI applications.

Let’s begin by understanding each of the two framework’s roles in building LLMs:

LLamaIndex: The Bridge between Data and LLM Power

LLamaIndex steps forward as an essential tool, allowing users to build structured data indexes, use multiple LLMs for diverse applications, and improve data queries using natural language.

It stands out for its data connectors and index-building prowess, which streamline data integration by ensuring direct data ingestion from native sources, fostering efficient data retrieval, and enhancing the quality and performance of data used with LLMs.

LLamaIndex distinguishes itself with its engines, which create a symbiotic relationship between data sources and LLMs through a flexible framework. This remarkable synergy paves the way for applications like semantic search and context-aware query engines that consider user intent and context, delivering tailored and insightful responses.


Learn all about LlamaIndex from its Co-founder and CEO, Jerry Liu, himself! 


LlamaIndex Features

LlamaIndex is an innovative tool designed to enhance the utilization of large language models (LLMs) by seamlessly connecting your data with the powerful computational capabilities of these models. It possesses a suite of features that streamline data tasks and amplify the performance of LLMs for a variety of applications, including:

Data Connectors:

  • Data connectors simplify the integration of data from various sources into the data repository, bypassing manual and error-prone extraction, transformation, and loading (ETL) processes.
  • These connectors enable direct data ingestion from native formats and sources, eliminating the need for time-consuming data conversions.
  • Advantages of using data connectors include automated enhancement of data quality, data security via encryption, improved data performance through caching, and reduced maintenance for data integration solutions.


  • LLamaIndex Engines are the driving force that bridges LLMs and data sources, ensuring straightforward access to real-world information.
  • The engines are equipped with smart search systems that comprehend natural language queries, allowing for smooth interactions with data.
  • They are not only capable of organizing data for expeditious access but also enriching LLM-powered applications by adding supplementary information and aiding in LLM selection for specific tasks.


Data Agents:

  • Data agents are intelligent, LLM-powered components within LLamaIndex that perform data management effortlessly by dealing with various data structures and interacting with external service APIs.
  • These agents go beyond static query engines by dynamically ingesting and modifying data, adjusting to ever-changing data landscapes.
  • Building a data agent involves defining a decision-making loop and establishing tool abstractions for a uniform interaction interface across different tools.
  • LLamaIndex supports OpenAI Function agents as well as ReAct agents, both of which harness the strength of LLMs in conjunction with tool abstractions for a new level of automation and intelligence in data workflows.


Read this blog on LlamaIndex to learn more in detail


Application Integrations:

  • The real strength of LLamaIndex is revealed through its wide array of integrations with other tools and services, allowing the creation of powerful, versatile LLM-powered applications.
  • Integrations with vector stores like Pinecone and Milvus facilitate efficient document search and retrieval.
  • LLamaIndex can also merge with tracing tools such as Graphsignal for insights into LLM-powered application operations and integrate with application frameworks such as Langchain and Streamlit for easier building and deployment.
  • Integrations extend to data loaders, agent tools, and observability tools, thus enhancing the capabilities of data agents and offering various structured output formats to facilitate the consumption of application results.


An interesting read for you: Roadmap Of LlamaIndex To Creating Personalized Q&A Chatbots


LangChain: The Flexible Architect for LLM-Infused Applications

In contrast, LangChain emerges as a master of versatility. It’s a comprehensive, modular framework that empowers developers to combine LLMs with various data sources and services.

LangChain thrives on its extensibility, wherein developers can orchestrate operations such as retrieval augmented generation (RAG), crafting steps that use external data in the generative processes of LLMs. With RAG, LangChain acts as a conduit, transporting personalized data during creation, embodying the magic of tailoring output to meet specific requirements.

Features of LangChain

Key components of LangChain include Model I/O, retrieval systems, and chains.

Model I/O:

  • LangChain’s Module Model I/O facilitates interactions with LLMs, providing a standardized and simplified process for developers to integrate LLM capabilities into their applications.
  • It includes prompts that guide LLMs in executing tasks, such as generating text, translating languages, or answering queries.
  • Multiple LLMs, including popular ones like the OpenAI API, Bard, and Bloom, are supported, ensuring developers have access to the right tools for varied tasks.
  • The input parsers component transforms user input into a structured format that LLMs can understand, enhancing the applications’ ability to interact with users.

Retrieval Systems:

  • One of the standout features of LangChain is the Retrieval Augmented Generation (RAG), which enables LLMs to access external data during the generative phase, providing personalized outputs.
  • Another core component is the Document Loaders, which provide access to a vast array of documents from different sources and formats, supporting the LLM’s ability to draw from a rich knowledge base.
  • Text embedding models are used to create text embeddings that capture the semantic meaning of texts, improving related content discovery.
  • Vector Stores are vital for efficient storage and retrieval of embeddings, with over 50 different storage options available.
  • Different retrievers are included, offering a range of retrieval algorithms from basic semantic searches to advanced techniques that refine performance.


A comprehensive guide to understanding Langchain in detail



  • LangChain introduces Chains, a powerful component for building more complex applications that require the sequential execution of multiple steps or tasks.
  • Chains can either involve LLMs working in tandem with other components, offer a traditional chain interface, or utilize the LangChain Expression Language (LCEL) for chain composition.
  • Both pre-built and custom chains are supported, indicating a system designed for versatility and expansion based on the developer’s needs.
  • The Async API is featured within LangChain for running chains asynchronously, reinforcing the usability of elaborate applications involving multiple steps.
  • Custom Chain creation allows developers to forge unique workflows and add memory (state) augmentation to Chains, enabling a memory of past interactions for conversation maintenance or progress tracking.


How generative AI and LLMs work


Comparing LLamaIndex and LangChain

When we compare LLamaIndex with LangChain, we see complementary visions that aim to maximize the capabilities of LLMs. LLamaIndex is the superhero of tasks that revolve around data indexing and LLM augmentation, like document search and content generation.

On the other hand, LangChain boasts its prowess in building robust, adaptable applications across a plethora of domains, including text generation, translation, and summarization.

As developers and innovators seek tools to expand the reach of LLMs, delving into the offerings of LLamaIndex and LangChain can guide them toward creating standout applications that resonate with efficiency, accuracy, and creativity.

Focused Approach vs Flexibility

  • LlamaIndex:
    • Purposefully crafted for search and retrieval applications, giving it an edge in efficiently indexing and organizing data for swift access.
    • Features a simplified interface that allows querying LLMs straightforwardly, leading to pertinent document retrieval.
    • Optimized explicitly for indexing and retrieval, leading to higher accuracy and speed in search and summarization tasks.
    • Specialized in handling large amounts of data efficiently, making it highly suitable for dedicated search and retrieval tasks that demand robust performance.
    • Offers a simple interface designed primarily for constructing search and retrieval applications, facilitating straightforward interactions with LLMs for efficient document retrieval.
    • Specializes in the indexing and retrieval process, thus optimizing search and summarization capabilities to manage large amounts of data effectively.
    • Allows for creating organized data indexes, with user-friendly features that streamline data tasks and enhance LLM performance.
  • LangChain:
    • Presents a comprehensive and modular framework adept at building diverse LLM-powered applications with general-purpose functionalities.
    • Provides a flexible and extensible structure that supports a variety of data sources and services, which can be artfully assembled to create complex applications.
    • Includes tools like Model I/O, retrieval systems, chains, and memory systems, offering control over the LLM integration to tailor solutions for specific requirements.
    • Presents a comprehensive and modular framework adept at building diverse LLM-powered applications with general-purpose functionalities.
    • Provides a flexible and extensible structure that supports a variety of data sources and services, which can be artfully assembled to create complex applications.
    • Includes tools like Model I/O, retrieval systems, chains, and memory systems, offering control over the LLM integration to tailor solutions for specific requirements.

Use Cases and Case Studies

LlamaIndex is engineered to harness the strengths of large language models for practical applications, with a primary focus on streamlining search and retrieval tasks. Below are detailed use cases for LlamaIndex, specifically centered around semantic search, and case studies that highlight its indexing capabilities:

Semantic Search with LlamaIndex:

  • Tailored to understand the intent and contextual meaning behind search queries, it provides users with relevant and actionable search results.
  • Utilizes indexing capabilities that lead to increased speed and accuracy, making it an efficient tool for semantic search applications.
  • Empower developers to refine the search experience by optimizing indexing performance and adhering to best practices that suit their application needs.

Case Studies Showcasing Indexing Capabilities:

  • Data Indexes: LlamaIndex’s data indexes are akin to a super-speedy assistant’ for data searches, enabling users to interact with their data through question-answering and chat functions efficiently.
  • Engines: At the heart of indexing and retrieval, LlamaIndex engines provide a flexible structure that connects multiple data sources with LLMs, thereby enhancing data interaction and accessibility.
  • Data Agents: LlamaIndex also includes data agents, which are designed to manage both “read” and “write” operations. They interact with external service APIs and handle unstructured or structured data, further boosting automation in data management.


langchain use cases
Source: Medium


Due to its granular control and adaptability, LangChain’s framework is specifically designed to build complex applications, including context-aware query engines. Here’s how LangChain facilitates the development of such sophisticated applications:

  • Context-Aware Query Engines: LangChain allows the creation of context-aware query engines that consider the context in which a query is made, providing more precise and personalized search results.
  • Flexibility and Customization: Developers can utilize LangChain’s granular control to craft custom query processing pipelines, which is crucial when developing applications that require understanding the nuanced context of user queries.
  • Integration of Data Connectors: LangChain enables the integration of data connectors for effortless data ingestion, which is beneficial for building query engines that pull contextually relevant data from diverse sources.
  • Optimization for Specific Needs: With LangChain, developers can optimize performance and fine-tune components, allowing them to construct context-aware query engines that cater to specific needs and provide customized results, thus ensuring the most optimal search experience for users.


Explore a hands-on curriculum that helps you build custom LLM applications!


Which Framework Should I Choose? LlamaIndex vs LangChain

Understanding these unique aspects empowers developers to choose the right framework for their specific project needs:

  • Opt for LlamaIndex if you are building an application with a keen focus on search and retrieval efficiency and simplicity, where high throughput and processing of large datasets are essential.
  • Choose LangChain if you aim to construct more complex, flexible LLM applications that might include custom query processing pipelines, multimodal integration, and a need for highly adaptable performance tuning.

In conclusion, by recognizing the unique features and differences between LlamaIndex and LangChain, developers can more effectively align their needs with the capabilities of these tools, resulting in the construction of more efficient, powerful, and accurate search and retrieval applications powered by large language models

March 1, 2024

RAG integration revolutionized search with LLM, boosting dynamic retrieval.

Within the implementation of a RAG system, a pivotal factor governing its efficiency and performance lies in the determination of the optimal chunk size. How does one identify the most effective chunk size for seamless and efficient retrieval? This is precisely where the comprehensive assessment provided by the LlamaIndex Response Evaluation tool becomes invaluable.

In this article, we will provide a comprehensive walkthrough, enabling you to discern the ideal chunk size through the powerful features of LlamaIndex’s Response Evaluation module. 

Tune in to Co-founder and CEO of LlamaIndex, Jerry Liu, and learn all about LLMs, RAG, fine-tuning and more!

Why chunk size matters in RAG system

Selecting the appropriate chunk size is a crucial determination that holds sway over the effectiveness and precision of a RAG system in various ways: 


Pertinence and detail:

Opting for a smaller chunk size, such as 256, results in more detailed segments. However, this heightened detail brings the potential risk that pivotal information might not be included in the most retrieved segments.

On the contrary, a chunk size of 512 is likely to encompass all vital information within the leading chunks, ensuring that responses to inquiries are readily accessible. To navigate this challenge, we will employ the faithfulness and relevance metrics.

These metrics gauge the absence of ‘hallucinations’ and the ‘relevancy’ of responses concerning the query and the contexts retrieved, respectively. 


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Generation time for responses:

With an increase in the chunk size, the volume of information directed into the LLM for generating a response also increases. While this can guarantee a more comprehensive context, it might potentially decelerate the system. Ensuring that the added depth doesn’t compromise the system’s responsiveness is pivotal.

Ultimately, finding the ideal chunk size boils down to achieving a delicate equilibrium. Capturing all crucial information while maintaining operational speed It’s essential to conduct comprehensive testing with different sizes to discover a setup that aligns with the unique use case and dataset requirements. 

Why evaluation? 

The discussion surrounding evaluation in the field of NLP has been contentious, particularly with the advancements in NLP methodologies.

Traditional evaluation techniques like BLEU or F1 are now unreliable for assessing models because they have limited correspondence with human evaluations.

As a result, the landscape of evaluation practices continues to shift, emphasizing the need for cautious application. 

In this blog, our focus will be on configuring the gpt-3.5-turbo model to serve as the central tool for evaluating the responses in our experiment.

To facilitate this, we establish two key evaluators, the faithfulness evaluator and the relevance evaluator, utilizing the service context. This approach aligns with the evolving standards of LLM evaluation, reflecting the need for more sophisticated and reliable evaluation mechanisms. 


 Faithfulness evaluator: This evaluator is instrumental in determining whether the response was artificially generated and checks if the response from a query engine corresponds with any source nodes. 

Relevancy evaluator: This evaluator is crucial for gauging whether the query was effectively addressed by the response and examines whether the response, combined with source nodes, matches the query. 

In order to determine the appropriate chunk size, we will calculate metrics such as average response time, average faithfulness, and average relevancy across different chunk sizes.  



Downloading dataset 

We will be using the IRS armed forces tax guide for this experiment. 

  • mkdir is used to make a folder. Here we are making a folder named dataset in the root directory. 
  • wget command is used for non-interactive downloading of files from the web. It allows users to retrieve content from web servers, supporting various protocols like HTTP, HTTPS, and FTP. 



Load dataset 

  • SimpleDirectoryReader class will help us to load all the files in the dataset directory. 
  • document[0:10] represents that we will only be loading the first 10 pages of the file for the sake of simplicity. 



Defining question bank 

These questions will help us to evaluate metrics for different chunk sizes. 




Establishing evaluators  

This code initializes an OpenAI language model (gpt-3.5-turbo) with temperature=0 settings and instantiate evaluators for measuring faithfulness and relevancy, utilizing the ServiceContext module with default configurations. 



Main evaluator method 

We will be evaluating each chunk size based on 3 metrics. 

  1. Average Response Time 
  2. Average Faithfulness 
  3. Average Relevancy 


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  • The function evaluator takes two parameters, chunkSize and questionBank. 
  • It first initializes an OpenAI language model (llm) with the model set to gpt-3.5-turbo. 
  • Then, it creates a serviceContext using the ServiceContext.from_defaults method, specifying the language model (llm) and the chunk size (chunkSize). 
  • The function uses the VectorStoreIndex.from_documents method to create a vector index from a set of documents, with the service context specified. 
  • It builds a query engine (queryEngine) from the vector index. 
  • The total number of questions in the question bank is determined and stored in the variable totalQuestions. 

Next, the function initializes variables for tracking various metrics: 

  • totalResponseTime: Tracks the cumulative response time for all questions. 
  • totalFaithfulness: Tracks the cumulative faithfulness score for all questions. 
  • totalRelevancy: Tracks the cumulative relevancy score for all questions. 
  • It records the start time before querying the queryEngine for a response to the current question. 
  • It calculates the elapsed time for the query by subtracting the start time from the current time. 
  • The function evaluates the faithfulness of the response using faithfulnessLLM.evaluate_response and stores the result in the faithfulnessResult variable. 
  • Similarly, it evaluates the relevancy of the response using relevancyLLM.evaluate_response and stores the result in the relevancyResult variable. 
  • The function accumulates the elapsed time, faithfulness result, and relevancy result in their respective total variables. 
  • After evaluating all the questions, the function computes the averages 




Testing different chunk sizes 

To find out the best chunk size for our data, we have defined a list of chunk sizes then we will traverse through the list of chunk sizes and find out the average response time, average faithfulness, and average relevance with the help of evaluator method. After this, we will convert our data list into a data frame with the help of Pandas DataFrame class to view it in a fine manner. 



From the illustration, it is evident that the chunk size of 128 exhibits the highest average faithfulness and relevancy while maintaining the second-lowest average response time. 

Use LlamaIndex to construct a RAG system 

Identifying the best chunk size for a RAG system depends on a combination of intuition and empirical data. By utilizing LlamaIndex’s Response Evaluation module, we can experiment with different sizes and make well-informed decisions.

When constructing a RAG system, it is crucial to remember that the chunk size plays a pivotal role. Therefore, it is essential to invest the necessary time to thoroughly evaluate and fine-tune the chunk size for optimal outcomes. 


You can find the complete code here